25 replies to this topic

[JustSteve]

.. And keep clothing to a minimum*



*this could be dangerous if you carry attractive passengers. A nice pair of jugs might become very distractive.

[Wil_h]

The way to improve the mpg, assuming the engine is set-up properly, is to do the following:

Fit narrow wheels and 145-section tyres, remove the wheel arch extensions, remove the big wing mirrors and replace with the small rectangular mirror only on the driver's side A-post near the top, drive with the windows closed, drive with the tank no more than 1/2 full, don't have a roof rack, drive in high gears without using full throttle, don't carry unnecessary weight around and don't have fat passengers.

I would say this is great advice if you do a lot of higher speed driving, where aerodynamics play a major role, but it won't make up the loss of mpg that the OP is asking about as non of these parameters have changed.

[jakejakejake1]

I'm already on 145 section tyres, very small arches, no extra weight onboard, nothing additional attached to the outside to increase drag. None of this has changed since i have had the car, yet my average MPG has nearly halved.

The airfilter is a K&N replacement type, which is fairly new and not clogged, this and the spark plugs, rotor arm, dizzy cap and HT leads were replaced around 6 months ago, when i first started noting my MPG, and i wouldn't have thought any of these would deteriorate that severely in that time space, they all look in good condition.

The tyres were a little low on air (about 20-25 psi), but as said i cant image that making such a huge difference.

The spark plugs are a little on the black side, but I wouldn't say they were overly rich.

I have attached a small bottle to the carb overflow to see if I'm losing any fuel out of that, and the same for the tank breather, and I'm going to keep an eye out for a leaking petrol cap.

Does anyone know the difference the ignition timing would make to fuel consumption?

Thanks for all the input

[jaydee]

The tyres were a little low on air (about 20-25 psi), but as said i cant image that making such a huge difference.

They make a HUGE difference, set them at 30 psi.

[Cooperman]

Timing must be correct, as must mixture.
Compressions must also be right too. A badly seated or slightly burned valve will screw up consumption.

[Wil_h]

The tyres were a little low on air (about 20-25 psi), but as said i cant image that making such a huge difference.

They make a HUGE difference, set them at 30 psi.

It won't be huge, but it will have an effect.

The timing will make a significant differance on cruise if your vac advance is not working, but not much differance in town. If the dizzy hasn't moved then the timing should be the same anyway (ignoring wear).

Plugs being black does indicate a rich mixture. what carb do you have? If it's a HIF there might be a problem with the choke seals. actually, whatever carb you have, check that the choke is properly closing.

[jakejakejake1]

I'm using a HS4, and I am aware of it running a bit rich at idle (using colour-tune), as it runs better throughout the rev range like this. But it has always been running a tad rich. I will lean it out a couple of flats and see if it affects consumption that much.
I will check the choke as well.
I also found the vac-advance pipe (where the smaller one fits inside of the larger rubber one) was leaking slightly, causing the vac-advance to not hold vacuum very well.
Sorted this by putting a smear of grease around the inner pipe before inserting it.
This could of made a difference as most of my driving is part throttle.

[jakejakejake1]

Well after pumping the tyres up, sorting the vacuum advance and driving (supposedly) economically it has had zero effect on my mileage.
Just filled up and calculated I was getting 23 MPG again.
I have no idea what is causing this low fuel efficiency, but i'm sure that something is amiss.
I checked the mixture again with the Colourtune and at idle it is fine, I lowered the idle speed as well to see if this had any effect.

Is there anyone in Bath (or close) who could help me do a compression test as I don't have the equipment :)
Thanks

[liamharries]

How are your brakes? my car suddenly started using a lot of fuel a couple of months ago and turned out to be the callipers not releasing properly so I was driving with the brakes on and to be honest i couldn't even tell.

[Ethel]

Brakes & geometry can have a big effect. A vacuum gauge would be a worthwhile investment. Not only would it show up if you are using more throttle, without realising, to compensate for binding brakes etc; it can also show up some engine faults.

http://www.secondcha.../public/186.cfm

[jakejakejake1]

I found the problem in the end, one of the exhaust valves wasn't seating correctly and this was causing the bad consumption. Since sorting that out the car has been fine.

Jake